Tunable Photodetectors via In Situ Thermal Conversion of TiS₃ to TiO₂

• Main Authors: Foad Ghasemi, Riccardo Frisenda, Eduardo Flores, Nikos Papadopoulos, Robert Biele, David Perez de Lara, Herre S. J. van der Zant, Kenji Watanabe, Takashi Taniguchi, Roberto D’Agosta, Jose R. Ares, Carlos Sánchez, Isabel J. Ferrer, Andres Castellanos-Gomez
• Format: Article
• Language: English
• Published: MDPI AG 2020-04-01
• Series: Nanomaterials
• Subjects: 2D materials; photodetectors; oxidation; TiS₃; TiO₂; Raman spectroscopy
• Online Access: https://www.mdpi.com/2079-4991/10/4/711

In two-dimensional materials research, oxidation is usually considered as a common source for the degradation of electronic and optoelectronic devices or even device failure. However, in some cases a controlled oxidation can open the possibility to widely tune the band structure of 2D materials. In particular, we demonstrate the controlled oxidation of titanium trisulfide (TiS₃), a layered semicon-ductor that has attracted much attention recently thanks to its quasi-1D electronic and optoelectron-ic properties and its direct bandgap of 1.1 eV. Heating TiS₃ in air above 300 °C gradually converts it into TiO₂, a semiconductor with a wide bandgap of 3.2 eV with applications in photo-electrochemistry and catalysis. In this work, we investigate the controlled thermal oxidation of indi-vidual TiS₃ nanoribbons and its influence on the optoelectronic properties of TiS₃-based photodetec-tors. We observe a step-wise change in the cut-off wavelength from its pristine value ~1000 nm to 450 nm after subjecting the TiS₃ devices to subsequent thermal treatment cycles. Ab-initio and many-body calculations confirm an increase in the bandgap of titanium oxysulfide (TiO_2-xS_x) when in-creasing the amount of oxygen and reducing the amount of sulfur.